A pure beta line source to assess hot particle effects in vitro.

A model system is presented for assessing the biological effects of inhomogeneous irradiation fields resulting from exposure to particulate radioactive matter (hot particles). The resulting harm per unit dose to tissue is qualitatively different from homogeneous irradiation sources because of specific hot particle effects such as wasting of dose to necrotic tissue (overkill) and formation of microlesions leading to growth stimulation in adjacent tissue. In the case of beta-emitters, many of the cells in adjacent tissue receive considerable sublethal doses. To assess the influence of local necrosis and growth stimulation on radiation transformation in vitro, a neutron activated short 90Y wire was attached to the bottom foil of a cell culture dish. The system achieves doses of up to 200 Gy h(-1) directly above the wire, rapidly falling off within a few mm to less than 0.5 Gy h(-1). Acute cell death of murine M3-1 cells was observed in the highest dose regions. Colony-forming ability as a function of distance from the wire was investigated. The surviving fraction decreased over several orders of magnitude between 3 and 10 mm from the wire. This report describes the physical characteristics of the model system and subsequent biological survival data for mammalian cell culture. It is a useful and versatile system for modeling inhomogeneous radiation field effects.